In the Fight Against Invasive Plant Species, Fire a Worthy Weapon

A member of the DuPage County Forest Preserve's burn crew using a drip torch to set a controlled burn at the Herrick Lake Forest Preserve. (DuPage County Forest Preserve)

Every fall and spring, the forest preserves of Cook and DuPage Counties conduct controlled burns to reclaim the native landscape, one historically conditioned by fire and subsequently altered by the activities of European settlers.

Long before Chicago’s population boom and glass-and-steel structures of today, the region and state consisted mainly of “prairies mixed with woodlands,” according to Nick Fuller, the natural resource project coordinator at DuPage County Forest Preserve. This was due to “lightning strikes that caused wildfires and, more so, Native Americans setting fires to manipulate the landscape,” Fuller said.

Native Americans used fire for several reasons, according to the U.S. Forest Service. They burned woodlands to improve visibility for hunting wild game and watching for enemy tribes. They also used fire to clear land for crops or to chart paths through thick brush.

When European settlers arrived, Chicago’s landscape began to change: Wildfires were suppressed and trees chopped down for building material. Without regularly lit fires, many prairies turned to forests. Settlers also brought non-native plants such as buckthorn and honeysuckle that overran the area – invasive plants the forest preserves are still fighting today.

Invasive plants like garlic mustard, which was brought over by European settlers, endanger native plant life. (Christopher Holden / Flickr)

“The European settlers removed fire, the one tool that could keep these plants in check or get them out of there,” said John McCabe, director of resource management at Cook County Forest Preserve. “That’s what we tell people about why we burn. These are fire-dependent communities that we’re managing.”

Today, native plant species make up less than half of the region’s plant life. In a fight for sunlight, space and nutrients, invasive species typically win.

Fighting with fire

According to McCabe, the Cook County Forest Preserve burned 5,444 acres – about 10 percent of the land it manages – during its last burn season, which recently wrapped up. In DuPage County, Fuller said the forest preserve burns an annual average of 1,500 acres.

The reason to conduct these burns varies by landscape. Burning prairies, for example, essentially maintains the habitat, which has adapted to fire over the decades.

The Cook County Forest Preserve's burn crew establishes a border of burnt ground around the area to be burned. (Joe Occhiuzzo)

“If we didn’t do controlled burns, we wouldn’t have prairies because the entire ecosystems depend on fire,” Fuller said. “If we stop, these areas will turn into eight-foot tall brush within 20 years.”

But curbing the spread of invasive species such as the buckthorn tree – which has become the overwhelmingly dominant tree species in the Chicago area – is a common goal.

In woodlands, the buckthorn threatens the future of native oak trees, a keystone species that provides a habitat and food for several animal species. Oak tree saplings need plenty of space to mature, but invasive plants like buckthorn are encroaching on their territory.

Oak trees are an example of a keystone species. They have a large impact on several organisms within their ecosystem. (Rob Watling / Flickr)

Fuller said when Europeans settled in the area, they cut down many oak trees, clearing the area and setting the stage for an “explosion of oak seedlings” that grew into the current oak tree population.

“The oak trees in the area are now about 200 years old, so they’re near the end of their life cycle,” Fuller said. “But our woodlands are closing in from invasive brush, so oak seedlings and saplings aren’t going to grow unless we’re maintaining openness. If we lose this keystone species, the whole ecosystem will collapse.”

Where there’s smoke …

Naturally, there’s inevitable risk associated with burning fires. This spring, the DuPage County Forest Preserve curtailed its controlled burns because southern winds ushering migratory birds came earlier than expected, Fuller said. A burn could potentially kill the birds or destroy their nesting sites.

Fuller said before each burn, forest preserve employees survey targeted areas for wildlife. They use homing beacons to attract endangered Blanding’s turtles or place “snake boards” on the ground, which warm up in the sun, attracting snakes from their burrows. Fuller said if there’s significant animal presence they will not burn, but that collateral damage is unavoidable in such situations.

“It’s always a balance,” he said. “But in the long run, if you didn’t do controlled burning, you’d have ecosystems disappearing and you’d potentially lose the entire species, instead of a few individuals.”

April 19, 2016: Less than half of the plant life found in the Chicago region is native to the area. As the Morton Arboretum's tree improvement specialist, it's Joe Rothleutner's job to make sure those native plants are protected.

April 30, 2015: One in five parkway trees in Chicago is threatened by the Emerald Ash Borer beetle. So what can people do to stop the shrinking of the region's tree canopy? The Morton Arboretum's CEO, Gerry Donnelly, joins us to talk about reversing tree loss.